<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>SlideDown</title>
    <script src="../jquery-3.4.1.js"></script>
    <style>
        .left div,
        .right div {
            width: 100%;
            height: 50px;
            padding: 5px;
            margin: 5px;
            float: left;
            border: 1px solid #ccc;
            display: none;
        }
        .left div {
            background: #bbffaa;
        }
        .right div {
            background: yellow;
        }
    </style>
</head>
<body>
    <h2>slideDown</h2>
    <div class="left">
        <h4>测试一</h4>
<!--        display:none-->
        <div id="a1">隐藏的内容</div>
        <button>点击slideDown显示动画</button>
    </div>
</body>
<script>
    $("button").click(function () {
        $("#a1").slideDown(3000)
    })
</script>
</html>